Buzzing sound under dash

[Stephen0523]

Hello. I hear a rather loud buzzing sound under the dash when the defrost or heater is on. It goes off when I turn off the car.
It is doing this on my 1993 and 1989 Sunbirds.

I am going to try and make an audio recording to post here is I can.

 

[93sunny]

There was a service campaign on this back in the early 90's. I had my 93 fixed under warrantee and it never happened again until about two years ago.

Since I am somewhat anal about my service records, I can provide more details... Service bulletin 43-81-35
Part kit 22638225

Im pretty sure it is just the timer mechanism that needs to be replaced